计算折扣？

Question

有3个表 - 折扣（折扣）客户（客户）和订单（订单）

折扣

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|id_discount | count_orders | percent_discount |
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|          1 |            5 |              1,5 |
|          2 |           10 |              2,5 |

客户

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|  id_client |    Name      |      Surname     |
------------------------------------------------
|          1 | Ivan         | Petrov           |
|          2 | Vasya        | Vasev            |

订单

------------------------------------------------
| id         |  order_sum   | id_client        |
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在给定客户订单数量的情况下，如何计算总金额的问题？如果订单总数为5及以上，则折扣为1.5％，如果为10及以上，则为2.5％。否则，没有折扣。提前致谢

Answer 1

为了使其正常工作，您还需要为0个订单打折。

插入Discount（count_orders，percent_discount）值（0,0）;

要查找具有给定ID的客户的折扣百分比，请执行以下操作：

select d.percent_discount
from Discount d
where d.count_orders = isnull(
       (select max(count_orders) 
       from Discount dI where count_orders <= (
           select count(1) from Orders oI where oI.id_client = 1)), 0)  

获取每个客户的折扣：

select c.id_client as client_id,
       (select d.percent_discount
       from Discount d
       where d.count_orders = isnull(
          (select max(count_orders) 
          from Discount dI where count_orders <= (
              select count(1) from Orders oI where oI.id_client = c.id_client)), 0)) as discount
from Clients c

结合使用选项查找每个订单的折扣价格：

select o.id,
c.name,
c.surname,
o.order_sum,
(o.order_sum - (o.order_sum * client_discount.discount / 100)) as sumWithDiscount
from Orders o join Clients c on o.id_client = c.id_client
    join (select cI.id_client,
                 (select d.percent_discount
                 from Discount d
                 where d.count_orders = isnull(
                     (select max(count_orders) 
                     from Discount dI where count_orders <= (
                           select count(1) from Orders oI where oI.id_client = cI.id_client)), 0)) as discount
          from Clients cI) as client_discount on client_discount.id_client = c.id_client 

Answer 2

您可以使用PROCEDURE和CURSOR来解决此问题：

DELIMITER $$
CREATE PROCEDURE `getDiscount`(IN _orderSum INT(11))
  BEGIN
    DECLARE countOrders INT(11) DEFAULT 0;
    DECLARE percentDiscount DOUBLE DEFAULT 0;
    DECLARE done INT(1);
    DECLARE cur CURSOR FOR SELECT count_orders, percent_discount FROM Discount ORDER BY count_orders DESC;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
    SET done = 0;
    OPEN cur;
    discountLoop: LOOP
      FETCH cur INTO countOrders, percentDiscount;
      IF done = 1 THEN LEAVE discountLoop; END IF;
      IF _orderSum >= countOrders THEN
          SELECT percentDiscount AS percent_discount FROM dual;
          SET done = 1;
      END IF;
    END LOOP discountLoop;
    CLOSE cur;
  END$$
DELIMITER ;